wifi: mac80211: describe return values in kernel-doc

Add descriptions for two return values for two functions
that are missing them.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Gregory Greenman <gregory.greenman@intel.com>
Link: https://lore.kernel.org/r/20230920211508.79307c341723.Ibae386f0354f2e215d4955752ac378acc2466b51@changeid


Signed-off-by: Johannes Berg <johannes.berg@intel.com>